Some embodiments disclosed herein relate generally to enhancing therapy. Impedance monitoring is often used with implantable medical devices and in external monitoring devices to determine physiologic conditions that are of clinical significance or interest. For example, intra-thoracic impedance measurements can give a good indication of the fluid status of patients, with decreases in impedance being indicative of increases in fluid content. Knowledge of a patient's long-term impedance measurements and changes therein are a valuable clinical indicator of a patient's health. Herein “intra-thoracic” means within or across a portion of a heart, lungs and/or the pulmonary bed. For example, a subcutaneous or sub-muscular electrode, a transvenous electrode, a pericardial electrode or the like is used to measure impedance values of a patient.
The accumulation of fluid may be an indication of a failing heart circulation or other medical conditions. There are several physiologic malfunctions or diseases that can cause or affect the accumulation of fluid. In general, fluid accumulation is a failure or over-response of the homeostatic process within the body. The body normally prevents the build up of fluids by maintaining adequate pressures and concentrations of salt and proteins and by actively removing excess fluid. Fluid accumulation can occur, for example, when the body's mechanisms for preventing fluid accumulation are affected by disease, such as heart failure, left-sided myocardial infarction, high blood pressure, altitude sickness, emphysema (all of which affect pressures), cancers that affect the lymphatic system, and diseases that disrupt the protein concentrations. As a result, providing an adequate monitor of the patient's fluid status can provide physicians and patients with a better diagnostic tool to manage disease.
Upon detection of predetermined impedance values indicating abnormal fluid accumulation, the patient can be notified to seek professional care. In this way, a clinician is able to proactively address the patient's fluid accumulation, which may be the result of cardiac decompensation during heart failure. This allows patients to receive professional care (e.g., medications like diuretics and beta blockers in heart failure patients) much sooner, thereby decreasing the likelihood of the fluid accumulation developing into a more serious condition.
Determining the impedance values at which to notify a patient can prove difficult. Generally, patients should be notified every time they are approaching a dangerously high fluid accumulation. However, notifying patients when they face less than dangerous fluid accumulation levels can result in the unnecessary consumption of time and resources. This can pose economic and cost challenges when the need to alert patients is multiplied over a large patient population.